Gas phase reactions of some positive ions with atomic and molecular hydrogen at 300 K

Energy- and Local-Gradient-Based Neural Network Method for Accurately Describing Long-Range Interaction: Application to the H2 + CO+ Reaction

The long-range interaction plays an important role in theoretically describing ion-molecule reaction. However, most energy-based neural network fitting methods usually introduce spurious long-range interactions. In this work, we propose an energy- and local-gradient-based neural network (ELGNN) method to fit potential energy surfaces (PESs). K-means clustering is employed to divide the whole configuration space into three regions: reactant asymptotic region, interaction region, and product asymptotic region. In the interaction region, only the energies of sampled points are computed, while in the asymptotic regions, the gradients of partially sampled configurations are calculated as well, and both the energies and energy gradients (if necessary) are used to fit long-range interactions. These regions are joined together by switching functions. The ELGNN method is first applied to fit the PES of the H₂ + CO⁺ reaction, which has significant long-range interactions. It is found that the ELGNN method works better than the energy-based NN method in describing long-range interactions. The dynamics and kinetics of the reaction are then investigated on the new PES.

High-resolution infrared action spectroscopy of the fundamental vibrational band of CN. JOURNAL OF MOLECULAR SPECTROSCOPY 2020;374:111375. [PMID: 33162609 PMCID: PMC7116308 DOI: 10.1016/j.jms.2020.111375]

Rotational-vibrational transitions of the fundamental vibrational modes of the ¹²C¹⁴N⁺ and ¹²C¹⁵N⁺ cations have been observed for the first time using a cryogenic ion trap apparatus with an action spectroscopy scheme. The lines P(3) to R(3) of ¹²C¹⁴N⁺ and R(1) to R(3) of ¹²C¹⁵N⁺ have been measured, limited by the trap temperature of approximately 4 K and the restricted tuning range of the infrared laser. Spectroscopic parameters are presented for both isotopologues, with band origins at 2000.7587(1) and 1970.321(1) cm^-1, respectively, as well as an isotope independent fit combining the new and the literature data.

The Reaction of Sulfur Dioxide Radical Cation with Hydrogen and its Relevance in Solar Geoengineering Models

SO₂ has been proposed in solar geoengineering as a precursor of H₂ SO₄ aerosol, a cooling agent active in the stratosphere to contrast climate change. Atmospheric ionization sources can ionize SO₂ into excited states of S O 2 · + , which quickly reacts with trace gases in the stratosphere. In this work we explore the reaction of H 2 D 2 with S O 2 · + excited by tunable synchrotron radiation, leading to H S O 2 + + H ( D S O 2 + + D ), where H contributes to O₃ depletion and OH formation. Density Functional Theory and Variational Transition State Theory have been used to investigate the dynamics of the title barrierless and exothermic reaction. The present results suggest that solar geoengineering models should test the reactivity of S O 2 · + with major trace gases in the stratosphere, such as H₂ since this is a relevant channel for the OH formation during the nighttime when there is not OH production by sunlight. OH oxides SO₂ , triggering the chemical reactions leading to H₂ SO₄ aerosol.

Origin band of the first photoionizing transition of hydrogen isocyanide

The photoelectron spectrum of the X1Σ+ → X+2Σ+ ionizing transition of hydrogen isocyanide (HNC) is measured for the first time at a fixed photon energy (13 eV). The assignment of the spectrum is supported by wave-packet calculations simulating the photoionization transition spectrum and using ab initio calculations of the potential energy surfaces for the three lowest electronic states of the cation. The photoelectron spectrum allows the retrieval of the fundamental of the CN stretching mode of the cationic ground state ([small nu, Greek, tilde]3 = 2260 ± 80 cm-1) and the adiabatic ionization energy of hydrogen isocyanide: IE(HNC) = 12.011 ± 0.010 eV, which is far below that of HCN (IE(HCN) = 13.607 eV). In light of this latter result, the thermodynamics of the HCN+/HNC+ isomers is discussed and a short summary of the values available in the literature is given.

Reactions of Sulfur- and Oxygen-Containing Anions with Hydrogen Atoms: A Comparative Study

Reactions of hydrogen atoms with small sulfur-containing anions, SCN^-, CH₃COS^-, C₆H₅COS^-, ^-SCH₂COOH, C₆H₅S^-, 2-HOOCC₆H₄S^-, and related oxygen-containing anions, OCN^-, CH₃COO^-, C₆H₅COO^-, HOCH₂COO^-, C₆H₅O^-, 2-HOOCC₆H₄O^-, have been studied both experimentally and computationally. The experimental results show that associative electron detachment (AED) is the only channel for the reactions. The rate constants for reactions between sulfur-containing anions and H atoms are generally higher than for the related oxygen-containing anions with the exception of the reaction of SCN^-. The generally higher reactivity of the sulfur anions contrasts with previous results where AED reactivity was found to correlate with reaction exothermicity. Density functional theory calculations indicate that the reaction enthalpies, the characteristics of the reaction potential energy surfaces, and other structural and electronic factors can influence the reaction rate constants. This study indicates that organic sulfur anions can be more reactive than related oxygen anions in the interstellar medium where hydrogen atoms are abundant.

Ion chemistry in the interstellar medium

We present an overview of the interstellar medium, including physical and chemical conditions, spectroscopic observations, and current challenges in characterizing interstellar chemistry. Laboratory studies of ion-atom reactions, including experimental approaches and instrumentation, are described. We also tabulate and discuss comprehensive summaries of ion-neutral reactions involving hydrogen, nitrogen, and oxygen atoms that have been studied since Sablier and Rolando's 1993 review.

Infrared spectra of NH2NO, NH2NO+, and NNOH+ and of the N2⋯H2O complex trapped in solid neon

When a Ne:H2:N2O mixture is co-deposited at 4.3 K with a beam of neon atoms that have been excited in a microwave discharge, NH2NO+ is stabilized in sufficient concentration for detection of five of its vibrational fundamentals. Their assignments are supported by isotopic substitution studies and by the results of unrestricted B3LYP/cc-pVTZ calculations. Electron recombination results in the stabilization of NH2NO, for which the previously reported argon-matrix assignments are confirmed and extended. The OH-stretching fundamental of NNOH+ also is present in the spectrum of the initial sample deposit, but because of proton sharing with the neon matrix is shifted 43.3 cm(-1) from the gas-phase band center. The OD-stretching fundamental of NNOD+ is identified for the first time in the present study. An absorption at 2311.1 cm(-1) is contributed by the NN-stretching vibration of a complex of N2, probably with an ionic species. On prolonged visible and near-ultraviolet irradiation of the deposit, absorptions of the binary N2...H2O complex become increasingly prominent.

Generation of hydrogen radicals for reactivity studies in Fourier transform ion cyclotron resonance mass spectrometry

An efficient technique for generation of H* (D*) radicals in Fourier transform ion cyclotron resonance (FTICR) mass spectrometry is described. The method allows the probing of the reactivity of gas-phase H* radicals towards various ions isolated in the cell of an FTICR mass spectrometer. Results on interactions of H* and D* radicals with trapped positive or negative C60 fullerene ions, as well as singly charged peptide ions, are presented. Hydrogen radical addition or H/D-exchange reactions between trapped ions and free H* (D*) radicals were observed. Potential implementation of the technique for probing the gas-phase three-dimensional structures of polyatomic ions is discussed as well.